9 6 
Brae her. — Observations on Euglena deses. 
The diurnal movements would cause one to expect corresponding 
changes in the appearance of the organism during the day, and accordingly 
drawings were made at various times to investigate the nature of these. 
Early in the morning they appear extended and active as they rise to 
the surface and are moving with continual amoeboid movements. Later in 
the day they appear rounded off, and at night the eyespot is completely 
hidden from view. 
If light were the only determining factor the above results would 
include all the daily movements of Euglena deses ; but its behaviour, as has 
already been stated, is considerably modified by the response of the organism 
to the action of the tide. 
If a patch of mud is watched immediately after the tide has receded 
from it, no Euglenae are visible. From about a half to one hour later the 
first make their appearance in small isolated groups, about a quarter of an 
Fig. 2. E. deses. Diurnal differences in appearance. (Mag. ioo times.) (i) Early morning 
(actively moving) ; (2) midday (lying still on mud surface); (3) night (rounded off). 
inch in diameter. With regard to the incoming tide, the Euglenae do not 
disappear into the mud before they are covered by the tide, but when a few 
ripples of the rising water have passed over the spot they burrow down, and 
the green colour quickly fades and does not reappear until after the water 
has gone back. 
It may be seen, therefore, that the intervention of the action of the 
tide alters to a considerable extent the simple diurnal movements dependent 
solely upon light, and one would expect to find much variation in the 
behaviour of the organism according as the two factors, light and tidal 
action, are reacting simultaneously or at different times. 
In order to keep the Euglenae under closer observation and yet under 
natural conditions, an apparatus was devised for producing a periodic tidal 
flow over a given area of mud. In main essentials this apparatus consisted 
of a tank which was filled and emptied automatically by means of siphons 
which had been so arranged as to produce a tide at the proper time. In 
Fig. 3 a drawing of the apparatus is shown. 
